1. Field of the Invention
This invention relates to bellows and, more particularly, to a novel and highly effective bellows especially adapted for actuating an air switch and having a greatly extended mean time between failures (MTBF).
2. Description of the Prior Art
In many environments, it is not safe to employ an electrical switch. For example, because of the danger of an electrical shock or even electrocution, occupants of a hot tub or sauna cannot safely operate an electrical switch. In such environments, it is customary to employ a pneumatic device that operates in response to manual pressure (the term as used herein refers to pressure applied not only by a hand but also by a foot or in any other way) to send a pressure pulse to a pressure switch mounted at some distance from the hot tub or sauna. The pressure switch (momentary or latching) can in turn control electrical apparatus for controlling valve positions, pump motors, temperature settings, etc.
FIG. 1 shows conventional structure. A bellows 10 comprises a first portion 12 that is flexible and a second or base portion 14 that is rigid. The base portion 14 is disk-shaped. The flexible portion 12 has an open end 16 formed with an annular groove 18 that accommodates the periphery of the disk-shaped base 14. An annular bead of glue 20 or other adhesive is applied to the junction between the periphery of the disk 14 and the annular groove 18 in order to form an airtight seal.
The device is actuated manually. For example, when a digit D such as a thumb or a finger of an operator presses on the flexible part 12 to depress it from the position shown in solid outline in FIG. 1 to the position shown in broken outline, a pressure pulse passes through an extension 22 extending away from the base 14 on the side thereof opposite the flexible part 12. The extension 22 is formed with a nipple 24 and an annular recess 26. A hollow air tube 28 fits over the nipple 24 and is received in the recess 26. The extension 22 has an air passage 30 that communicates with the space 32 enveloped by the flexible portion 12 and the disk 14 and that communicates also with the air tube 28. This delivers a pressure pulse to a pressure switch 32, which operates in a conventional manner to control a valve or perform some other desired function.
One problem with this conventional structure is that, when the digit D depresses the flexible portion 12 from the position shown in solid outline in FIG. 1 to the position shown in broken outline, the increased air pressure that results within the space 32 is transmitted throughout the space, applying an outward force to the part of the flexible portion 12 that is joined to the base 14 and tending to flex and disrupt the seal formed by the glue 20. Also, the mechanical transmission of force from the digit D through the wall of the portion 12 to the area of the seal tends to flex and disrupt the seal. After a number of cycles of operation the bellows may fail. Another problem is that the tube 28 may become detached from the nipple 24, as when the device is withdrawn from a wall for inspection or repair.